Technical Field
The present invention relates to a peptide nucleic acid for anti-subgroup J avian AVIAN LEUKOSIS VIRUS and uses thereof.
Related Art
Avian leukosis is a class of infectious diseases caused by avian leukosis virus (ALV) and characterized by malignant proliferation of hematopoietic cells, including lymphoid leukosis (LL), erythroblastic leukosis, myeloblastic leukosis, and myeloid leukosis. Among them, LL causes the greatest hazard to the poultry industry. According to the characteristics of viral envelope, the virus neutralization assay, the host range, and the molecular biological properties of the genome, the virus is classified into 10 subgroups, i.e. subgroups A to J, including all the retroviruses causing neoplastic diseases of poultry except for reticuloendotheliosis virus (REV). The subgroups A, B, C, and D are exogenous viruses, and the subgroups E, F, G, H, and I are endogenous viruses. The subgroups A and B are the exogenous virus subgroups that are mostly commonly found in commercial eggs (Leghorn chickens), the subgroups C and D have an extremely low infection rate and can scarcely be detected, and the subgroup E includes the prevalent low-pathogenic and non-pathogenic endogenous viruses. The subgroup J was initially isolated from commercial generation broilers by Payne and his coworkers in 1988, which is an exogenous leukosis virus that can be widely transmitted horizontally and vertically in the chicken flock when recombined with the endogenous subgroup E. All the breeds of broilers are susceptible to ALV-J; however, the tumor incidence rates of infected chickens differ significantly. Although the layers may be infected with ALV-J, tumor is seldom caused upon natural infection. With the increasingly growth of the poultry industry, the incidence of suspected ALV-J are more wide, causing a high death rate and culling rate of the attacked chicken flock, and bringing a heavy economic loss to the poultry farm.
The disease was epidemic worldwide in 1998, and caused a heavy blow to the poultry industry worldwide. In 1999, the ALV-J virus was initially isolated from and detected in commercial generation broilers by Du Yan et al in China. Since 2000, leukosis subgroup J becomes highly epidemic in the chicken flocks in China, and exhibits an expanded host range. The vertical and horizontal transmission of the virus leads to a clinical and subclinical infection, thus causing a high economic loss.
The economic loss caused by avian leukosis mainly includes the following two aspects: elicitation of tumors, causing the death of chickens; and elicitation of non-neoplastic diseases, causing subclinical infection resulting from immunosuppression, as manifested by emaciation and anemia, tolerant viremia, and immunosuppression of chickens, thereby seriously affecting the poultry production. ALV-J infection may lead to multiple infections of chickens, and several different viruses may be detected simultaneously in individual sick chickens, for example, Reticuloendotheliosis virus (REV), infectious bursal disease viruses (IBDV), and chicken infectious anemia virus (CIAV). During practical production, generally only the impact of tumogenesis on production is noticed, and the subclinical infection is generally ignored. Immunosuppression may include atrophy or agenesia of lymphoid organ, hypergammaglobulinemia, reduced blastocyte formation induced by mitogenic agents and decreased antibody response. Therefore, the loss caused by ALV to the poultry industry is mainly attributed to the earlier non-neoplastic diseases (immunosuppression), and the later death caused by tumors is just a surface phenomenon of immunosuppression from quantitative change to qualitative change.
The clinical symptoms of sick chickens mainly include inappetence, progressive emaciation, abnormal plumage, poor mental state of sick chickens, abdominal distention of some chickens, tangible enlarged liver, pale crest and wattle, crest atrophy of some chickens, visible blood blisters of 1-3 cm on heads, backs, chests, legs, and wings of some chickens that appear brownish purple, touch soft, are elastic to some degree, and have a clear boundary between them and the surrounding skin, unceasing bleeding after rupture of the blood blisters, and contamination of plumage around the blood blisters by large area of blood.
Immunosuppression refers to the fact that the response of an organism to an antigen is low and even deficiency due to the influence arising from various factors (e.g. nutrition, disease, and challenge, etc). The immunosuppression caused by viruses is particularly serious, thus forming immunosuppression. ALV-J may cause myeloid tumors in adult broilers, leading to a high death rate, and cause the reproductivity to decrease (due to the influence on the development of breeding rooster). Due to the death and decreased reproductivity of breeding pullet, the eggs for hatch are reduced, causing a heavy loss to the broiler industry. In addition to the primary infection causing death of chickens, ALV, more importantly, invades immune organs by, for example, causing serious damage to thymus, bursa of Fabricius, and other major immune organs of chickens, resulting in reduced function of the immune organs and decreased resistance to diseases of the organisms, and finally leading to complications and secondary infections. Moreover, it is difficult to eliminate the immunosuppression caused by ALV-J, such that the chicken flocks are unable to respond to or less respond to vaccination, causing failed immunization and thus the outbreak of highly infectious diseases.
Virions have a diameter of 80-100 nm, and are composed of an exterior envelope and an interior nucleocapsid having dense electrons, where the core structure is a regular icosohedron and comprises diploid RNA, nucleocapsid, reverse transcriptase, integrase, and protease. The virus envelope has radial protrusions with a diameter of about 8 nm thereon. The genome of ALV is about 7.2 kb long, and may be directly used as mRNA. The structure of ALV gene is gag-pol-env from 5′ to 3′ terminus, which encode viral structural proteins, RNA dependent DNA polymerase (reverse transcriptase) and membrane glycoproteins respectively. The gag gene encodes the non-glycosylated structural proteins in the virus, including matrix protein, protease, capsid, and nucleocapsid. In ALV subgroups, these viral proteins are highly conserved and have high homology, that is, the so-called group specific antigen (GSA). The pol gene encodes the reverse transcriptase and integrase of the virus, to complete the integration of viral RNA to proviral DNA and proviral DNA into the cell chromosome, before the cell gene information expression. The env gene encodes the glycosylated proteins on the viral envelope, including the surface glycoprotein subunit (SU) gp85 and transmembrane glycoprotein subunit (TM) gp37. SU is encoded by the gp85 gene and comprises a virus-receptor determinant determining the specificity of avian leukosis subgroups. TM is response for the transformation of virus into the cells. The long terminal repeats (LTRs) at two sides of the structural gene are correlated with the replication and translation of the viral RNA. The acute transforming ALV also carries a virus-oncogene (v2oncogene). The virus contains 5 structural proteins, that is, Viral group specific antigen capsid protein P27, viral basement membrane protein P19, nucleocapsid protein P12 involved in RNA processing and package, aspartase P15 involved in cleavage of protein precursor, and P10 with unknown functions. The endogenous virus strain RAV-0 has variant P27, namely P27°.
Antisense nucleic acid is a fragment of naturally occurring or artificially synthesized nucleotide sequence that is complementary to a sequence of a target gene (mRNA or DNA), and specifically binds to the viral target gene by base pairing, to form a hybrid molecule, thus playing a role in the regulation of target gene expression at the level of replication, transcription, or translation, or induction of RNase H to recognize and cleave mRNA, such that the function of mRNA is lost.
The antisense nucleic acid includes antisense RNA and antisense DNA, and is characterize by convenient synthesis, simple sequence design, easy modification, high selectivity, and high affinity. As a new anti-viral and anti-tumor agent, the antisense nucleic acid arouses a revolution in the field of pharmacology, that is, new reactions post drug-receptor binding are initiated by a new drug receptor mRNA through the new binding pattern to the receptor (Watson-Crick crossing), including: (1) degradation of the target RNA mediated by RNase H; and (2) inhibition on the DNA replication and transcription and post-transcriptional processing and translation, etc. It is believed that the antisense oligonucleotide (ODNs) therapy is more specific than the conventional drug therapies. Since the late 1970s, the antisense nucleic acid drugs have gone out of the laboratory, and put into practical clinical use in the over three decades of years. The antisense therapy receives great attention especially after the first antisense nucleic acid drug Fomivirsen is approved by FDA.
The mechanism of action of antisense nucleic acid is that based on the principle of base pairing, it is involved in the regulation of relevant gene expression by binding to the target RNA through base pairing. The modes of action may include the following. (1) The anti-sense RNA is bound to the viral mRNA, to from a complementary duplex, thus blocking the binding of ribosome to viral mRNA, and inhibiting the translation of viral mRNA into proteins. (2) The anti-sense DNA can form a triple helix nucleic acid with the target gene, and regulate the transcription of a gene by acting on the transcript, enhancer and primer region controlling the gene transcription. (3) The binding of the antisense nucleic acid to the viral mRNA can prevent the transport of the mRNA to cytoplasm. (4) After the binding of the antisense nucleic acid to the viral mRNA, the mRNA are more easily recognized and degraded by the nuclease, thus greatly reducing the half life of mRNA. The four pathways of action may all be embodied as the inhibition or regulation for viral gene expression, and the regulation is highly specific.
The antisense nucleic acid recognizes the targeting gene based on the principle of base complementation and pairing. Theoretically, for example, the chromosome of animal cells has about several billions of pairs of bases. If the number of the 4 bases (A, G, C, and T) are substantially the same and distributed at random in the whole gene, then the antisense nucleic acid of greater than 17 bases is unlikely to hybridize to a non-target gene according to the principle of statistics. Therefore, the binding of the antisense nucleic acid molecule of greater than 17 bases to the target gene is unique, such that the antisense nucleic acid is highly specific.
Studies show that a copy of gene in the cell can produce 200-300 mRNAs, from which 100,000 biologically active protein molecules are translated. The conventional drugs mainly act on several sites on a domain of the protein molecule having biological functions. Actually, the protein structure is very complex and the spatial structure of active proteins in an organism is versatile. It is difficult to achieve a desirable effect by controlling the dynamics and overall functions of the target molecules via the limited several sites on which the conventional drugs act. Therefore, the limitation of the conventional drugs is obvious. Several dozens to hundreds of protein may be translated from the mRNA, and the target gene is directly regulated by the antisense nucleic acid at the mRNA level, which means that the efficacy of the conventional drugs is increased by several dozens to hundreds of times. It can be seen that the regulation by antisense nucleic acid is quite economic and reasonable.
Toxicological research shows that the antisense nucleic acid has an extremely low toxic in vivo. Although the antisense nucleic acid may remain in vivo for a long or short period of time, it is finally removed by degradation, through which the hazard caused by integration of an exogenous gene into the chromosome of a host in a transgenic therapy is avoided. Compared with the conventional drugs, the antisense nucleic acid drugs have the advantages of high specificity, high efficacy, and low toxic effect, and are useful in the inhibition of tumor growth and viral replication. Currently, numerous drugs become available in American and European markets, and additional 30 antisense nucleic acid drugs are under preclinical study or under phases I, II, and III trial after development.
Due to the large existence of exonucleases in animals, the antisense nucleic acid is quickly degraded and loses the activity if it is not chemically modified. At present, the antisense nucleic acid may be chemically modified through many methods, for example, the common modification of an antisense nucleic acid with phosphorthioate and 2′-methoxy. Moreover, the modification of drugs with phosphorthioate is well studied, and it can effectively resist the degradation by nuclease, and contributes to the activity of the nucleaseRase H. Currently, this modification method is successfully used with the antisense nucleic acid drugs in clinic. However, these are merely modification method for the first generation of antisense nucleic acids. With the development and progression of technologies, new routes and methods of modification will be developed, which allows the research of the second and third generations of antisense nucleic acids to be carried out. Among them, the modification of peptide nucleic acids receives the greatest attention.
Peptide nucleic acids (PNAs) are new analogs of DNA that have neutral amide bonds in the backbone, and can specifically target the groove in DNA. The structural component is N(2-aminoethyl)-glycine, and the bases are attached via methylenecarbonyl to the amino N of the backbone. PNAs are the second generation of antisense nucleic acids.